Many patent applications directed to three piece solid golf balls have been filed, but balls which are superior to two piece solid golf balls, especially in impact resilience, flying properties, durability and hitting feeling, have not been developed yet. Three piece solid golf balls which has a large size and good properties are more desired.
Japanese Kokoku Publication No. 61029/1988 proposes that a specific gravity of a center core is higher than that of an outer layer, and a diameter of the center core is made larger in order to impart high impart resilience and good hitting feeling to the three piece golf ball. Sufficient specific gravity difference can be obtained in small size golf balls, but it is difficult to impart good properties to large size golf balls. Durability of a golf ball is apt to be reduced in the large size three piece solid golf ball.
Japanese Kokai Publication (unexamined) 181069/1987 also proposes that the center core is made soft and reduces its diameter to 24 to 29 mm to impart a specific gravity difference between the center core having a high specific gravity and the outer layer having a low specific gravity. The proposed golf balls, however, are inferior to conventional two piece solid golf balls in impact resilience and flying distance. Also, since the center core of the golf balls is prepared from TMPT (U.S. Pat. No. 3,313,545) which is rarely employed for golf balls, durability is poor.
In order to provide high impact resilience and good hitting feeling, Japanese Kokai Publication No. (unexamined) 241464/1985 proposes that a specific gravity difference is formed between the center core having a high specific gravity and the outer layer having a low specific gravity and the center core is made softer to lower moment of inertia of a golf ball. The golf ball has improved feeling when it is hit, however is inferior to a two piece golf ball in impact resilience.
The present inventors have found that the proposed methods are all suitable for a small size three piece solid golf ball, but are not suitable for large size one. In other words, the large size three piece solid golf balls needs unique constructions which are different from small size one.